This invention relates to differential amplifiers which are a form of operational amplifiers and are employed in connection with the amplification and comparison of signals. Basically, differential amplifiers comprise two amplifying elements having, respectively, one electrode connected to an electrode of the other amplifier, separate voltages being applied at the control electrodes thereof which, where required, shall be compared with one another.
In a differential amplifier of known construction (cf. "Elektronik," 1970, No. 5, pp. 145-148) bipolar transistors are used as amplifying elements. The amplifier is part of an integrated circuit, and, thus, is comparatively small. However, a differential amplifier constructed in this manner cannot readily be applied to modern integrated circuits comprising metal oxide semiconductor (MOS) transistors.
A differential amplifier circuit is known which comprises field effect transistors disposed in the input circuit (cf. "Electronics," June 21, 1971, pp. 76-80) wherein one of two voltages being compared is applied to the gate electrodes thereof. However, at the output a conventional output amplifier is connected downstream of the field effect transistors. The output amplifier is composed of bipolar transistors, so that this known differential amplifier cannot readily be applied to integrated circuits in conjunction with the MOS transistors widely used at the present time.
An object of the invention is, therefore, to provide a differential amplifier of very simple construction, which can readily be used for integration in a circuit arrangement comprising MOS transisitors.